[Interpreter] Optimize equality check with null/undefined with a check on the map.

src/interpreter/interpreter.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/interpreter/interpreter.h"
 
 #include <fstream>
 #include <memory>
 
 #include "src/ast/prettyprinter.h"
@@ skipping 1919 matching lines @@
 }
 
 // TestInstanceOf <src>
 //
 // Test if the object referenced by the <src> register is an an instance of type
 // referenced by the accumulator.
 void Interpreter::DoTestInstanceOf(InterpreterAssembler* assembler) {
   DoCompareOp(Token::INSTANCEOF, assembler);
 }
 
+// TestUndetectable <src>
+//
+// Test if the value in the <src> register equals to Null/Undefined. This is
+// done by checking undetectable bit on the map of the object.
+void Interpreter::DoTestUndetectable(InterpreterAssembler* assembler) {
+  Node* reg_index = __ BytecodeOperandReg(0);
+  Node* object = __ LoadRegister(reg_index);
+
+  Label not_equal(assembler), end(assembler);
+  // If the object is an Smi then return false.
+  __ GotoIf(__ TaggedIsSmi(object), &not_equal);
+
+  // If it is a HeapObject, load the map and check for undetectable bit.
+  Node* map = __ LoadMap(object);
+  Node* map_bitfield = __ LoadMapBitField(map);
+  Node* map_undetectable =
+      __ Word32And(map_bitfield, __ Int32Constant(1 << Map::kIsUndetectable));
+  __ GotoIf(__ Word32Equal(map_undetectable, __ Int32Constant(0)), &not_equal);
+
+  __ SetAccumulator(__ BooleanConstant(true));
+  __ Goto(&end);
+
+  __ Bind(&not_equal);
+  {
+    __ SetAccumulator(__ BooleanConstant(false));
+    __ Goto(&end);
+  }
+
+  __ Bind(&end);
+  __ Dispatch();
+}
+
 // Jump <imm>
 //
 // Jump by number of bytes represented by the immediate operand |imm|.
 void Interpreter::DoJump(InterpreterAssembler* assembler) {
   Node* relative_jump = __ BytecodeOperandImm(0);
   __ Jump(relative_jump);
 }
 
 // JumpConstant <idx>
 //
@@ skipping 840 matching lines @@
   __ StoreObjectField(generator, JSGeneratorObject::kContinuationOffset,
       __ SmiTag(new_state));
   __ SetAccumulator(old_state);
 
   __ Dispatch();
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8